Patterned metal thermal interface

ABSTRACT

The present invention is a patterned metal thermal interface. In one embodiment a system for dissipating heat from a heat-generating device includes a heat sink having a first surface adapted for thermal coupling to a first surface of the heat generating device and a thermal interface having at least one patterned surface, the thermal interface being adapted to thermally couple the first surface of the heat sink to the first surface of the heat generating device. The patterned surface of the thermal interface allows the thermal interface to deform under compression between the heat sink and the heat generating device, leading to better conformity of the thermal interface to the surfaces of the heat sink and the heat generating device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 11/619,928, filed Jan. 4, 2007, which is herein incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to microprocessor and integratedcircuits, and relates more particularly to the cooling of integratedcircuit (IC) chips.

BACKGROUND OF THE INVENTION

Recent years have seen an evolution toward higher-power microprocessor,graphics, communication and memory semiconductor chips. This evolutionin turn has driven interest in highly conductive solder thermalinterface (STI) materials and liquid metal thermal interface (LMI)materials to provide improved thermal coupling between a chip and a heatsink. In both cases, it is an essential function of the thermalinterface material that it thermally couple and adhere both to the chipand to the heat sink, in order to reduce the occurrence of failure inuse (e.g., due to poor heat transfer between the chip and the heatsink).

A distinguishing feature of STI materials (which are understood toinclude low-melt solder materials that are solid at room temperature butmay at least partially melt at normal chip process temperatures) is thatthey are composed of metal or metal alloys, such as gallium, indium,tin, lead or bismuth, among others. In some cases, these materials canattack or diffuse into other materials such as aluminum or copper, whichare common heat sink materials. In other cases, these materials may failto wet other materials such as silicon, silicon dioxide, silicon nitrideor the like, which are common chip materials. De-wetting or degradationof the interface between the STI material and the heat sink, or betweenthe STI material and the chip, can produce local hot spots that impedethe thermal performance or cause outright failure of the chip inhigh-power applications. It is therefore desirable to provide a wettingor adhesion layer between a thermal interface material and a chip and/orbetween a thermal interface and a heat sink that maintains barrierproperties and also isolates these mating surfaces from corrosive andadverse intermetallic formation with the interface metal.

Finally, both STI and LMI interfaces are conventionally applied inliquid phase. This requires the management of containment, voidformation and intermetallic formations that are characteristic of liquidphase interactions. This is often difficult or impractical to achieve.Moreover, in cases where melting points exceed 125 degrees Celsius,attaching a heat sink would likely result in component failure.

Thus, there is a need for a metal thermal interface that provides goodthermal coupling between a chip and a heat sink without the complicatingneed to enter liquid phase.

SUMMARY OF THE INVENTION

The present invention is a patterned metal thermal interface. In oneembodiment a system for dissipating heat from a heat-generating deviceincludes a heat sink having a first surface adapted for thermal couplingto a first surface of the heat generating device and a thermal interfaceformed a soft metal and having at least one patterned surface, thethermal interface being adapted to thermally couple the first surface ofthe heat sink to the first surface of the heat generating device.Patterning refers to an arrangement of local thick and thin spots on anotherwise flat foil or sheet of metal interface material. Many patternsare possible, and the precise distribution of thick and thin spots ischosen based on the application to give statistical uniformity. Thepatterned surface of the thermal interface allows the thermal interfaceto deform under compression between the heat sink and the heatgenerating device, leading to better conformity of the contact points ofthe thermal interface to the surfaces of the heat sink and the heatgenerating device.

The size and distribution of the thick and thin spots in the patterningis selected to account for the bow, warp and other surface properties ofthe heat generating device and of the heat sink. For instance, in anexemplary embodiment, the relative thickness between the thick and thinspots on the patterned thermal interface is 150 micron, with 200 micronpitch in a rectangular periodic array for an expected heat sink warpingof approximately fifty micrometers

During compression of the thermal interface (e.g., between theheat-generating device and the heat sink) the surface patterning of thethermal interface allows for local high pressure points uniformlydistributed over the surface to be thermally coupled. This pressurecauses the soft metal to creep and conform microscopically to thesurfaces being thermally coupled, thereby providing good thermal contactat these points. Thermal coupling is further enhanced by the breakup ofsurface oxides, allowing metallic bonds to form at contact pointsbetween the metal interface material and the metal of the surfaces beingthermally coupled. In one embodiment, moderate heat (e.g., not in excessof the thermal interface's melting point) is applied to accelerate thecreep process. Embodiments of the invention intend that the thermalinterface metal remain in solid phase during application and use.

In one embodiment, surface oxides of the thermal interface and of thecontact surfaces of the heat generating device and the heat sink aremanaged in any one or more of a variety of ways. For example, in oneembodiment, the thermal interface is fabricated immediately prior to usein order to limit the thickness of surface oxide. In another embodiment,at least one of the contact surfaces of the heat generating device, theheat sink and the thermal interface is treated with at least one of: anacid, a base, a plasma clean, a chemical cleaning agent or a mechanicalabrasive. The treatment removes surface oxides prior to join or assemblyof the heat sink assembly components. In another embodiment at least oneof the contact surfaces of the heat generating device, the heat sink andthe thermal interface is treated with at least one of: hydrochloricacid, oxalic acid, acetic acid, isopropyl alcohol, methyl alcohol, ethylalcohol, acetone, and xylene. In yet another embodiment, at least one ofthe contact surfaces of the heat generating device, the heat sink andthe thermal interface is treated with at least one of: sand blasting,sand paper, metal wool, cryogenic clean, and burnishing. In anotherembodiment still, at least one of the contact surfaces of the heatgenerating device, the heat sink and the thermal interface is treatedwith at least one of: reactive ion etch, plasma ashing, chemical downstream etching.

Since most heat sinks are clamped to heat-generating devices withsignificant force (e.g., 20 pounds or more) in order to compress thermalgreases, the patterned metal thermal interface provides a practical highperformance alternative with little or no change to existing assemblies.Pressure and optional heating are present during the application of thepatterned metal interface. Once the thermal interface has been appliedand bonded to the heat-generating device and to the heat sink, optionalmaintenance of pressure leads to better mechanical stability androbustness of the assembly. Reducing the amount of surface oxide on allmating surfaces of the heat-generating device and the heat sink prior toassembly further improves the thermal performance of the thermalinterface.

The patterned metal thermal interface is intended as a general thermalinterface solution. One particular area in which the thermal interfaceof the present invention may find use is between a computer chipcomprised of silicon (and typically coated with silicon dioxide orsilicon nitride) and a heat sink comprised of copper, nickel-platedcopper or aluminum. A second area in which the thermal interface of thepresent invention may find use is between a lidded computer chip and aheat sink (similar to the heat sink described above), where the lid ofthe computer chip is comprised of copper or nickel-plated copper. Thus,the mating surfaces to be thermally coupled will, in many cases, becomprised of copper, nickel or silicon. In one embodiment, where thepatterned metal thermal interface is comprised of indium or tin, thethermal interface can be directly applied to copper, nickel and siliconsurfaces. In another embodiment, where the patterned metal thermalinterface is comprised of silicon, a surface metallization is optionallyapplied to promote bonding and improve the thermal contact performance.If pressure is maintained during use, surface metallization of thethermal interface is not absolutely necessary, but will improve thethermal performance and reduce corrosion susceptibility.

In the most minimal embodiment, a patterned metal sheet is placedbetween heat-generating device and a heat sink and compressed withlittle or no surface preparation. For example, a patterned indium foilof approximately 200 micron thickness can be placed between a copperheat sink and a nickel-plated lidded computer chip in an assembly thatexerts pressure on the foil sufficient to cause creep in the foil. Inthis configuration, there would be little bonding due to surface oxides,and both the thermal performance and the corrosion resistance of thethermal interface would be less than optimal. However, this performanceis acceptable in most use cases. The thermal interface material willcontinue to creep during operation and is enhanced by the heat ofoperation. Creep will continue until an asymptotic stability is reached.

In addition to the thermal advantages of using the patterned metalthermal interface, there are advantages in rework. One of the mostcommon thermal interface materials in use today is thermal grease.Thermal grease comprises oil containing thermally conductive particles.Thermal grease is extremely messy and difficult to clean during rework.The patterned metal thermal interface, by contrast, is dry andconvenient to remove during rework by simply separating the heat sinkfrom the heat-generating device and peeling or lightly scraping thepatterned metal thermal interface off of the coupled surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited embodiments of theinvention are attained and can be understood in detail, a moreparticular description of the invention, briefly summarized above, maybe had by reference to the embodiments thereof which are illustrated inthe appended drawings. It is to be noted, however, that the appendeddrawings illustrate only typical embodiments of this invention and aretherefore not to be considered limiting of its scope, for the inventionmay admit to other equally effective embodiments.

FIG. 1 is an exploded view of a heat sink assembly using a patternedmetal thermal interface, according to one embodiment of the presentinvention;

FIG. 2 is a plan view illustrating one embodiment of the thermalinterface illustrated in FIG. 1, according to the present invention;

FIG. 3 is a flow diagram illustrating one embodiment of a method forassembling a heat sink assembly, according to the present invention;

FIG. 4 is a schematic diagram illustrating one embodiment of theassembled heat sink assembly illustrated in FIG. 1, where the heat sinkassembly is assembled according to the method illustrated in FIG. 3;

FIG. 5 is a flow diagram illustrating a second embodiment of a methodfor assembling a heat sink assembly, according to the present invention;

FIG. 6 is a schematic diagram illustrating one embodiment of theassembled heat sink assembly illustrated in FIG. 1, where the heat sinkassembly is assembled according to the method illustrated in FIG. 5; and

FIG. 7 is an exploded view illustrating one embodiment of a heat sinkassembly, in which the adhesion/wetting/bonding layers comprise aninsert or film that is separately formed and then applied to the heatsink assembly.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

DETAILED DESCRIPTION

In one embodiment, the present invention is a thermal interface for usein dissipating heat from heat-generating devices (e.g., microprocessorchips). Embodiments of the present invention provide improved heattransfer from a heat generating device to a heat sink, thereby allowingfor better heat dissipation from the heat generating device. Thisultimately results in better performance of the heat generating device,as heat-related failures are minimized.

FIG. 1 is an exploded view of a heat sink assembly 100 using a patternedmetal thermal interface 102, according to one embodiment of the presentinvention. As illustrated, the heat sink assembly 100 comprises thethermal interface 102 disposed between a heat generating device 104(e.g., a microprocessor chip or a lidded chip) and a heat sink 106.Alternatively, the heat sink 106 may be a lid where the heat generatingdevice 104 is a microprocessor or semiconductor chip.

The heat sink 106 comprises a base 108 having first surface 108 a and asecond surface 108 b. In one embodiment, the heat sink 106 comprises atleast one of: a vapor chamber, a heat pipe or a liquid cooler. The firstsurface 108 a of the base 108 is relatively flat and is configured tocontact the thermal interface 102. To this end, the first surface 108 aoptionally comprises a first interface metallization layer 110. In oneembodiment, the first interface metallization 110 layer comprises anadhesion layer and a wetting layer (i.e., such that the adhesion layeris “sandwiched” between the wetting layer and the first surface 108 a ofthe base 108). For example, one embodiment of the first interfacemetallization layer 110 comprises a film of gold (wetting layer)deposited over a film of titanium (adhesion layer). In furtherembodiments, the adhesion layer comprises at least one of: titanium, atitanium-tungsten alloy, chromium, nickel, molybdenum or tantalum. Infurther embodiments, the wetting layer comprises at least one of:platinum, gold, an oil or an organic material. In a further embodiment,the first interface metallization layer 110 has a total thickness ofapproximately 2500 Angstroms, where the adhesion layer accounts forapproximately 2000 Angstroms and the wetting layer accounts forapproximately 500 Angstroms.

Many other embodiments of the first interface metallization layer 110are possible. In one embodiment, the materials (i.e., for the adhesionand wetting layers) and thickness of the first interface metallizationlayer 110 are chosen such that: (1) the adhesion layer substantiallyadheres to the first surface 108 a of the base 108; (2) the adhesionlayer substantially isolates first surface 108 a of the base 108 fromchemical interaction; (3) the adhesion layer does not form substantialadverse intermetallics with the thermal interface 102; (4) the adhesionlayer forms a metallic bond with the thermal interface 102 under heatand pressure; (5) the wetting layer substantially prevents oxideformation on the adhesion layer; (6) the wetting layer substantiallyadheres to the adhesion layer; and (7) the wetting layer issubstantially malleable and bonds to the thermal interface 102. Therespective thicknesses of the adhesion layer and the wetting layer arechosen with knowledge of the deposition process (e.g., sputtering,evaporation, jet process, etc.) to provide adhesion, coverage and lowfilm stress.

Thus, in practice, the first interface metallization layer 110 providesa surface that is able to be bonded to a heat-generating device.Moreover, it is noted that in the case of metallic thermal interfaces,the more noble the metals that the thermal interface 102 is sandwichedbetween, the less susceptible the thermal interface 102 is to corrosion.

In a further embodiment, a transition layer is provided between theadhesion or barrier layer portion of the first interface metallizationlayer 110 and the wetting layer in order to create a diffuse boundary.

In a further embodiment, the first interface metallization layer 110comprises a single metallic coating. For example, in one embodiment, thesingle coating comprises one of: gold, platinum, nickel, chrome ortungsten. In one embodiment, the material comprising the first interfacemetallization layer 110 is a more noble material than the materialcomprising the thermal interface 102. This is particularly advantageousin cases where bonding of the thermal interface 102 to the heat sink 106and/or heat-generating device 104 is not required, and the heat sinkassembly 100 is to be clamped with reasonable mechanical force for theduration of its useful lifetime.

In one embodiment, one or more of the surfaces of the heat sink 106,heat-generating device 104 and thermal interface 102 is coated with abonding agent, such as an organic polymer adhesive, an epoxy resin or anoil. For example, in one embodiment, a thin (e.g., 100 nm) coating ofepoxy is applied to the heat sink 106 and to the heat-generating device104. The thermal interface 102 is then placed between theheat-generating device 104 and the heat sink 106, and mechanical forceand heat are applied to compress the thermal interface 102 and to curethe bonding agent.

In another embodiment, no such coating is used. In this case, thethermal interface 102 is compressed between the heat-generating device104 and the heat sink 106. This embodiment is advantageous in lesshostile environments, where corrosion is less of a concern. Thisembodiment is also advantageous when the heat sink assembly 100 is to beclamped with mechanical force for the duration of its useful lifetime,but the advantages are not limited to this situation. For instance,advantages to the no coating embodiment may be realized where the heatsink 106 and the heat-generating device are made of compatible metals,and particularly where some degree of bonding can take place. A specificexample is a patterned indium thermal interface compressed between acopper heat sink and a nickel-coated heat-generating device. In thisexample, best results occur when care is taken to remove or minimizesurface oxides prior to compression, and when heat is applied duringinitial compression as described further herein.

In one embodiment, the second surface 108 b of the base 108 is alsorelatively flat and comprises a plurality of fins 112 ₁-112 _(n)(hereinafter collectively referred to as “fins 112”) coupled thereto.The fins 112 are positioned in a substantially perpendicular orientationrelative to the base 108.

The heat generating device 104 also comprises a first surface 104 a anda second surface 104 b. In one embodiment, both the first surface 104 aand the second surface 104 b of the heat generating device 104 arerelatively flat. The first surface 104 a of the heat generating device104 further comprises a second interface metallization layer 114. In oneembodiment, the second interface metallization layer 114 is constructedin a manner similar to the first interface metallization layer 110 andcomprises an adhesion layer and a wetting layer. In a furtherembodiment, a transition layer is provided between the adhesion layer ofthe second interface metallization layer 114 and the wetting layer inorder to create a diffuse boundary.

The thermal interface 102 comprises a patterned metal foil, a metal meshor a perforated metal sheet. The metal of the thermal interface is asolid metal (i.e., solid in phase). The foil is comprised of arelatively soft metal that deforms readily under moderate pressure. Inone embodiment, the foil is comprised of at least one of: indium, lead,gold, silver, bismuth, antimony, tin, thallium or gallium. In anotherembodiment, the thermal interface 102 is comprised of a soft metal mesh.The thermal interface 102 is patterned or textured; that is, the thermalinterface 102 exhibits a substantially uniform thickness and flatnessbut with local topography (high and low spots). In a further embodiment,the thermal interface 102 has a thickness of approximately 150 microns.

FIG. 2 is a plan view illustrating one embodiment of the thermalinterface 102 illustrated in FIG. 1, according to the present invention.As illustrated, the surface of the thermal interface 102 is patterned ortextured. In one embodiment, the pattern carried on the thermalinterface 102 comprises one of many potential patterns. In oneembodiment, the pattern has a topography that comprises high spots(e.g., spot 200) and low spots (e.g., spot 202). In a furtherembodiment, the pattern has a topology that allows for at leastapproximately fifty percent compression of the thermal interface 102when the thermal interface 102 is pressed between a heat generatingdevice and a heat sink. For example, in one embodiment, the pattern is awaffle pattern. In another embodiment, the pattern is a line pattern. Inyet another embodiment, the pattern comprises at least approximately 100microns of topology in parallel grooves, with approximately 0.5 mmpitch.

The use of the patterned thermal interface illustrated in FIGS. 1 and 2provides improved heat transfer from the heat generating device 104 tothe heat sink 106, thereby allowing for better heat dissipation from theheat generating device 104. Specifically, when pressed between the heatgenerating device 104 and the heat sink 106, the patterned thermalinterface 102 deforms, allowing the thermal interface 102 to conform tothe first surface 104 a of the heat generating device 104 and to thefirst surface 108 a of the heat sink base 108. Thus, heat generated bythe heat generating device 104 is transferred to the base 108 of theheat sink 106, via the patterned thermal interface 102. The base 108then spreads the heat to the fins 112 of the heat sink 106, from whichthe heat is carried by forced air (generated, e.g., by fans, not shown).The better the thermal coupling between the heat generating device 104and the heat sink 106, the more heat that is dissipated by the heat sinkassembly 100.

FIG. 3 is a flow diagram illustrating one embodiment of a method 300 forassembling a heat sink assembly, according to the present invention. Themethod 300 may be implemented, for example, to assemble a heat sinkassembly such as the heat sink assembly 100 illustrated in FIG. 1.

The method 300 is initialized at step 302 and proceeds to step 304,where the method 300 coats a first surface of a heat generating devicewith an adhesion film. The adhesion film comprises a film of materialthat does not alloy to an appreciable extent with the material of thethermal interface. In one embodiment, the adhesion film comprised atleast one of: titanium, a titanium-tungsten alloy, chromium, nickel,molybdenum or tantalum. In one embodiment, the adhesion film is vacuumdeposited. The method 300 then proceeds to step 306 and coats theadhesion film with a wetting film. In one embodiment, the wetting filmcomprises at least one of: gold or platinum. In one embodiment, thewetting film is vacuum deposited, in order to limit the amount of oxygenpresent when the wetting film material is applied to the adhesion film.The adhesion and wetting films together provide an interfacemetallization layer for the heat generating device. In an alternativeembodiment, the adhesion/wetting film can be bulk evaporated orsputtered in reverse order onto a backing material (e.g., a polyimide)and then bonded (via pressure and/or heat) to the first surface of theheat generating device using a bonding agent (e.g., epoxy). The backingmaterial would then be peeled away to reveal the wetting film surface.In this embodiment, care is taken to achieve a bond line ofapproximately 250 nanometers. Further embodiments include applying theadhesion/wetting film by plating, plasma spray or jet process.

In step 308, the method 300 coats a first surface of a heat sink with anadhesion film. In one embodiment, the adhesion film is vacuum deposited.The method 300 then proceeds to step 310 and coats the adhesion filmwith a wetting film. In one embodiment, the wetting film is vacuumdeposited, in order to limit the amount of oxygen present when thewetting film material is applied to the adhesion film. The adhesion andwetting films together provide an interface metallization layer for theheat generating device. In an alternative embodiment, theadhesion/wetting film can be bulk evaporated or sputtered in reverseorder onto a backing material (e.g., a polyimide) and then bonded (viapressure and/or heat) to the first surface of the heat sink using abonding agent (e.g., epoxy). The backing material would then be peeledaway to reveal the wetting film surface. In this embodiment, care istaken to achieve a bond line of approximately 250 nanometers.

In step 312, the method 300 positions a patterned metal thermalinterface (such as the thermal interface illustrated in FIGS. 1 and 2)between the heat generating device and the heat sink. Specifically, thethermal interface is positioned between the first surface of the heatgenerating device and the first surface of the heat sink, both of whichhave been coated with an interface metallization layer as describedabove. In an alternative embodiment, the patterned metal thermalinterface is pre-applied to the heat sink (e.g., by the heat sinkmanufacturer) prior to assembly in accordance with the method 300. Inthis case, the thermal interface may be patterned as part of the joiningprocess to the heat sink (e.g., with a die or heated die). In oneembodiment, the thermal interface is comprised of an indium foil. In oneembodiment, the thermal interface has a thickness in the range ofapproximately 100 to 200 microns (e.g., approximately 150 microns). Inone embodiment, the thermal interface is processed prior to deploymentin the heat sink assembly in order to minimize surface oxides. In oneembodiment, this processing involves rolling and patterning the thermalinterface just prior to deployment to expose the oxide free metal. Inanother embodiment, the processing involves treating the thermalinterface with a dilute acid, such as hydrochloric acid.

In step 314, the method 300 applies pressure to the heat sink assembly(i.e., the heat generating device, the heat sink and the thermalinterface), in order to compress the thermal interface between the heatgenerating device and the heat sink. This pressure deforms the patternedthermal interface, allowing the thermal interface to conform to thefirst surface of the heat generating device and the first surface of theheat sink at a near-atomic scale. In one embodiment, the amount ofpressure applied to the heat sink assembly is on the order ofapproximately ten to twenty kg/cm². In one embodiment, the heat sink isfurther held in place using screws, polymer glue, clips or otherappropriate fastening means.

In optional step 316 (illustrated in phantom), the method 300 appliesheat to the heat sink assembly. The application heat in addition to thecontinued application of pressure accelerates the alloying of thewetting film with the thermal interface material, resulting in a solidjoint of the thermal interface material and the adhesion film material.In one embodiment, the heat applied to the heat sink assembly is in therange of approximately forty degrees Celsius to approximately 135degrees Celsius. For example, in one embodiment, the heat applied to theheat sink assembly is on the order of approximately eighty-five degreesCelsius.

The method then terminates in step 320.

The method 300 thereby produces a heat sink assembly in which intimatecontact is maintained between the thermal interface and the heatgenerating device, and between the thermal interface and the heat sink.In one embodiment, this contact comprises a continuous materialconnection that is mechanically and thermally stable due to themetallurgic effects of the pressure and heat applied thereto. Duringoperation of the heat generating device, the thermal interface willtypically remain clamped and under modest pressure between the heatgenerating device and the heat sink.

When fully compressed, the thermal interface will likely exhibit smallbreaks perpendicular to the interface plane as a result of incompletecollapse of the pattern carried on the thermal interface. These breaksallow the thermal interface material to expand and contract in responseto thermal stresses, without generating large shear forces relative tothe heat generating device and the heat sink. Thus, such discontinuitiesallow the conformed thermal interface to tolerate expansion differencesbetween itself, the heat generating device and the heat sink, all ofwhich are generally comprised of different materials having differentthermal expansion properties.

In an alternative embodiment, rather than coating the surfaces of theheat generating device and the heat sink with the interfacemetallization layers, a bonding agent (e.g., epoxy) is applied to one ormore of: the thermal interface, the first surface of the heat generatingdevice and the first surface of the heat sink. The components areassembled, and the interface is then pressed and cured by theapplication of the heat. In this case, a thin bond line (e.g.,approximately 250 nanometers or less in thickness) is maintained. In afurther embodiment, the heat sink is first cleaned of most surfaceoxides before bonding, and heat is applied for a period of hours (e.g.,approximately ten to twenty hours) at a temperature in the range ofapproximately forty degrees Celsius to approximately 135 degrees Celsius(e.g., approximately ninety degrees Celsius). Bonding provides theadvantages of convenience, speed and simplicity; however, coating withan interface metallization layer provides better resistance tocorrosion.

Those skilled in the art will appreciate that many materials other thantitanium and gold may be used to form the interface metallization layer.In general, any material or combination of materials that provides: (1)good adherence to the heat generating device and the heat sink; (2)limited solubility and limited intermetallic activity with respect tothe thermal interface material; (3) limited surface oxidation(potentially achieved by capping a first material with a noble metal);and (4) ready alloying to the thermal interface material (againpotentially achieved by capping a first material with a noble metal).

FIG. 4 is a schematic diagram illustrating one embodiment of theassembled heat sink assembly 100 illustrated in FIG. 1, where the heatsink assembly 100 is assembled according to the method 300 illustratedin FIG. 3. As illustrated, the thermal interface 102 is compressedbetween the heat generating device 104 and the heat sink 106 such thatthe thermal interface conforms to the surfaces of the heat generatingdevice 104 and the heat sink 106.

FIG. 5 is a flow diagram illustrating a second embodiment of a method500 for assembling a heat sink assembly, according to the presentinvention. The method 500 may be implemented, for example, to assemble aheat sink assembly such as the heat sink assembly 100 illustrated inFIG. 1.

The method 500 is initialized at step 502 and proceeds to step 504,where the method 500 positions a thermal interface between a firstsurface of a heat generating device and a patterned first surface of aheat sink. In one embodiment, the thermal interface comprises asubstantially flat, smooth metal foil. In one embodiment, the foil iscomprised of indium. The first surface of the heat sink is patternedwith a relief structure.

In step 506, the method 500 applies pressure to the heat sink assembly,such that the thermal interface is compressed between the first surfaceof the heat generating device and the first surface of the heat sink.Compression causes the first surface of the heat sink to impress thepattern carried thereon into the thermal interface, locally deformingthe thermal interface and allowing the thermal interface to conform tothe first surface of the heat generating device and the first surface ofthe heat sink at a near-atomic scale. In one embodiment, the heat sinkis further held in place using screws, polymer glue, clips or otherappropriate fastening means.

In optional step 508 (illustrated in phantom), the method 500 appliesheat to the heat sink assembly before terminating in step 510.

An advantage of the method 500 is that is allows direct thermal couplingof vapor chamber heat sinks to high-power semiconductor ormicroprocessor chips without requiring the high temperatures normallyneeded for solder attachment. Moreover, compliant metal interfaces maybe used without vacuum chip metallization in the case of organicbonding. Ultimately, these advantages result in improved thermalperformance in the range of two to five mm² C/W.

FIG. 6 is a schematic diagram illustrating one embodiment of theassembled heat sink assembly 100 illustrated in FIG. 1, where the heatsink assembly 100 is assembled according to the method 500 illustratedin FIG. 5. As illustrated, the thermal interface 102 is compressedbetween the heat generating device 104 and the heat sink 106 such thatthe thermal interface conforms to the surfaces of the heat generatingdevice 104 and the heat sink 106.

FIG. 7 is an exploded view illustrating one embodiment of a heat sinkassembly 700, in which the adhesion/wetting/bonding layers comprise aninsert or film 710 that is separately formed and then applied to theheat sink assembly 700. As illustrated, the film 710 may be positionedbetween the thermal interface 702 and a first surface 704 a of the heatgenerating device 704. Alternatively, the film 710 may be positionedbetween the thermal interface 702 and a first surface 708 a of the heatsink 708. Moreover, the film 710 may be formed with any combination ofone or more of the adhesion layer, the wetting layer and the bondinglayer.

Thus, a thermal interface is disclosed that provides improved heattransfer from a heat generating device to a heat sink, thereby allowingfor better heat dissipation from the heat generating device. Thisultimately results in better performance of the heat generating device,as heat-related failures are minimized.

While foregoing is directed to the preferred embodiment of the presentinvention, other and further embodiments of the invention may be devisedwithout departing from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A system for dissipating heat from a heat generating device,comprising: a heat sink having a first surface adapted for thermalcoupling to a first surface of the heat generating device; and a solidmetal thermal interface having at least one patterned surface, thethermal interface being adapted to thermally couple the first surface ofthe heat sink to the first surface of the heat generating device.
 2. Thesystem of claim 1, wherein a thickness and a flatness of the at leastone patterned surface are substantially uniform, but the patternedsurface exhibits local thick spots and thin spots.
 3. The system ofclaim 2, wherein the thermal interface comprises a soft metal thatdeforms readily under pressure.
 4. The system of claim 3, wherein thethermal interface comprises at least one of: a patterned foil, a metalmesh, or a perforated metal sheet.
 5. The system of claim 2, wherein thethermal interface comprises indium.
 6. The system of claim 2, whereinthe thermal interface comprises lead.
 7. The system of claim 2, whereinthe thermal interface comprises gold.
 8. The system of claim 2, whereinthe thermal interface comprises silver.
 9. The system of claim 2,wherein the thermal interface comprises bismuth.
 10. The system of claim2, wherein the thermal interface comprises antimony.
 11. The system ofclaim 2, wherein the thermal interface comprises tin.
 12. The system ofclaim 2, wherein the thermal interface comprises thallium.
 13. Thesystem of claim 2, wherein the thermal interface comprises gallium. 14.The system of claim 2, wherein the at least one patterned surface has atopography that allows for at least fifty percent compression of thethermal interface when the thermal interface is compressed between theheat generating device and the heat sink.
 15. The system of claim 1,wherein the at least one patterned surface includes breaks that allowthe thermal interface to expand and contract in response to thermalstress.
 16. The system of claim 1, wherein the thermal interface iscompressed between the first surface of the heat sink and the firstsurface of the heat generating device.
 17. The system of claim 16,wherein the at least one patterned surface conforms to the first surfaceof the heat sink and to the first surface of the heat generating deviceto form a continuous material connection.
 18. The system of claim 1,wherein a solid joint exists between the first surface of the thermalinterface and the first surface of the heat sink.
 19. The system ofclaim 1, wherein the first surface of the heat sink comprises a reliefpattern that matches the at least one patterned surface.
 20. A systemcomprising: a heat generating device; a heat sink having a first surfaceadapted for thermal coupling to a first surface of the heat generating,device; and a solid metal thermal interface compressed between the firstsurface of the heat generating device and the first surface of the heatsink, the thermal interface having at least one patterned surface, thethermal interface being adapted to thermally couple the first surface ofthe heat sink to the first surface of the heat generating device.